On 6/24/19 11:33 PM, Poul-Henning Kamp wrote:
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In message <[email protected]>, jimlux writes:
and, as well, COSMIC-2 is being deployed - 6 satellites each carrying a
fancy GPS receiver that does two things: Precision Orbit Determination
(POD) using a choke ring antenna; Occultation measurements of the
atmosphere using a directive array of helical antennas facing the limb.
How do you orient a choke ring antenna in space ? Is the distance
for LEO to GNSS orbits long enough that you can still just "point
it upwards" ?
Yes,up, or at the limb, depending on which satellites you want to see.
Or a combination of two antennas which are canted from each other, but
generally "up" (which is what COSMIC-2 does)
GPS receivers that are doing reflectometry/scatterometry have their
antennas pointed down
GNSS is at 20,000 km, LEO is 500-1000 km, so the geometry isn't much
different.
It's when you get to MEO or GEO that which way you point the antenna
becomes important. You're typically adding some gain (because the link
is 60,000km instead of 20,000).
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